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Status

Current state: [One of "Under Discussion", "Accepted", "Rejected"]

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Sometimes, application's threads will block for max.block.ms to send records using KafkaProducer#send. It exhausted threads of whole system for the time in some cases.

When application try to reduce the max.block.ms to decrease the blocking time. Thus, they will find they couldn't change the value to any one which is smaller than the time costed for metadata's fetch. What's more, metadata's fetch is one heavy operation which cost a lot of time.

Take our project as example. we will take about 4 seconds to complete the metadata's fetch. So, we can't change the max.block.ms to any value < 4000ms.

After analyzing the issue. The root cause is the configured max.block.ms is shared by "metadata fetch" operation and "append record" operation. We can refer to follow table in detail:

What's more, the metadata's fetch only need to done one time in whole blocking of KafkaProducer#send. After the complete of fetch, the metadata will be retrieved from cache directly and its timer update only happen on network thread.

So this KIP try to reach the goal we can change the max.block.ms to wanted smaller value without worry about the metadata's fetch.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.